1. Technical Field
An aspect of the present invention relates to an image forming apparatus having a fixing unit to thermally fix a transferred image onto a recording sheet.
2. Related Art
An image forming apparatus to form an image electrophotographically is often provided with a fixing device, which thermally fixes a toner image transferred to a recording sheet thereon. For example, a fixing device including a heat roller to heat the recording sheet with the toner image and a pressure roller to press the recording sheet against the heat roller are known. As the recording sheet is fed in between the heat roller and the pressure roller, the toner image is thermally fixed onto the recording sheet.
When smaller-sized recording sheets, smaller than axial lengths of the rollers, such as postcards, are fed in the fixing device, a part of the heat roller which does not contact the recording sheets retains heat, and temperature in the part may increase to be higher than temperature in the remaining part which contacts the recording sheet. If the temperature is excessively increased, bearings to hold the heat roller may melt and deformed. In order to avoid such deformation, therefore, the fixing device may be equipped with a heat sensor, which senses the temperature of the heat roller so that the fixing operation in the fixing device can be ceased when the sensor detects excessively increased temperature in the heat roller.